[January 15, 2013]WASHINGTON
(AP) -- At some point on Inauguration Day, if all goes as expected, the president's limousine will slow to a stop on its journey down Pennsylvania Avenue from the Capitol to the White House. A Secret Service agent will open the rear passenger door, and the newly sworn-in president and the first lady will emerge from his car for a several-minute stroll. The crowd will cheer. Barack Obama will wave.

In that moment, Pennsylvania Avenue is America's red carpet. And the president and first lady are the only celebrities on it. The victory walk has become an iconic inaugural moment, one expected by the public and the press.

And though the tradition dates only to President Jimmy Carter, it has already developed an air of inevitability and predictable patterns.

Charlie Brotman, who has been the announcer for the inaugural parade for decades, says the crowd never tires of the moment. When it happens, the 85-year-old says, spectators can expect to hear him saying something like this over the loudspeakers: "Ladies and gentleman, here's what the parade is all about. The president of the United States is walking right in front of you."

Carter wasn't thinking about starting a tradition when he decided to walk the mile-plus parade route in 1977. The idea wasn't even his. Before the inauguration, a Wisconsin senator sent Carter a letter suggesting the new president walk the route to set a good example for physical fitness. Carter initially dismissed the idea as silly, but soon reconsidered. He wrote in his memoir, "Keeping Faith," that he "began to realize that the symbolism of our leaving the armored car would be more far-reaching than simply to promote exercise."

"I wanted to provide a vivid demonstration of my confidence in the people as far as security was concerned, and I felt a simple walk would be a tangible indication of some reduction in the imperial status of the president and his family," he wrote.

Carter told only a few people of his plan, including the Secret Service, and spectators were shocked when he emerged from the limo. At first, revelers seemed to think something was wrong with the car. Then, they realized what was happening.

"There were gasps of astonishment and cries of 'They're walking! They're walking!'" Carter remembered in his memoir.

No other president has again walked the entire route, a trek that took Carter 40 minutes. His successor, Ronald Reagan, is the only modern president to skip the stroll. Reagan and his wife, Nancy, stuck their heads out of their limo's sun roof during part of the drive in 1981, and Reagan didn't have a chance to walk after his second inauguration in 1985: that parade was canceled because of cold weather.

The next four presidents, two Democrats and two Republicans, have all pounded Pennsylvania Avenue pavement. They generally walk at least the last block to the White House, though the length and the timing of the strolls have varied. Once the president and his wife emerge, however, the script is similar. Waving, thumbs-up-giving and hand-holding are standard, and the first lady always seems to make the trek in heels. Even rain or cold don't seem to dissuade presidents. George W. Bush braved wet weather and temperatures in the 30s to walk with his wife, Laura, in 2001.

Whether children accompany their parents is hard to predict. Amy Carter, then 9, jumped and danced down the street with her parents. Chelsea Clinton joined her parents in 1997 when she was 16.

More predictable is a heavy Secret Service presence. Former agents say the parade can be a security challenge, mainly because everyone knows the route, and the street is less secure than the limo. But agents also understand the president wants to get out and be seen, says former agent Joseph Petro, who wrote a book about his years protecting presidents. Agents take a host of precautions, including leaving the limo doors open, just in case the president has to get back inside quickly.

During his last inauguration, the Obamas walked about six blocks. The president and first lady left their limo near the National Archives and Records Administration building, where the original Constitution, Bill of Rights and Declaration of Independence are displayed. After walking several blocks, Michelle Obama in green heels, they returned to the car briefly. They re-emerged for the last stretch to the White House, to a second round of wild cheers.